Data head and method using a single antiferromagnetic material to pin multiple magnetic layers with differing orientation

ABSTRACT

Methods of fabricating spin valve sensors in accordance with the invention include forming a pinning layer from an antiferromagnetic material and forming a synthetic antiferromagnet adjacent the pinning layer. A free ferromagnetic layer is formed, and exchange tabs are formed adjacent outer portions of the free ferromagnetic layer for biasing the free layer. The exchange tabs are formed from the same antiferromagnetic material as the first pinning layer. Then, the magnetic moments of the synthetic antiferromagnet are set, and the magnetic moment of the free ferromagnetic layer is biased, during a single anneal in the presence of a single magnetic field.

[0001] The present invention claims priority to Provisional ApplicationSerial No. 60/119,772, filed Feb. 11, 1999 and entitled METHOD OF USINGA SINGLE ANTIFERROMAGNETIC MATERIAL TO PIN MULTIPLE MAGNETIC LAYERS WITHDIFFERING ORIENTATIONS.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to data storage systems. Morespecifically, the present invention relates to data storage systemsusing read heads, which utilize multiple magnetic layers with differingmagnetic orientations.

[0003] There is ever increasing demand for high data densities thatrequire sensitive sensors to read data from a magnetic media. Advancedgiant magnetoresistive (GMR) spin valve sensors that hare increasedsensitivity are replacing anisotropic magnetoresistive (AMR) sensors. Aspin valve sensor consists of two soft magnetic layers separated by athin conductive, non-magnetic spacer layer such as copper. Anantiferromagnetic material (called the “pinning layer”) is placedadjacent to the first soft magnetic layer to prevent it from rotating.Antiferromagnetic materials exhibiting this property are termed “pinningmaterials”. With its rotation inhibited, the first soft layer is termedthe “pinned layer”. The second soft layer rotates freely in response toan external field and is called the “free layer”. If the pinning layeris deposited before the free layer, the structure is called a “bottomspin valve” or “BSV”. The layers can also be deposited in reverse orderwith the pinning layer on the top, in which case it is called a “topspin valve” or “TSV”.

[0004] The sensor must be stabilized against the formation of edgedomain walls because domain wall motion results in electrical noise,which makes data recovery impossible. A common way to achieve this iswith a permanent magnet abutted junction design. In this scheme,permanent magnets with high coercive field (i.e., hard magnets) areplaced at each end of the sensor. The field from the permanent magnetsstabilizes the sensor and prevents edge domain formation, as well asprovides proper bias.

[0005] Abutted junctions are difficult to engineer for the followingreasons. To properly stabilize the sensor, the magnet must provide moreflux than can be absorbed by the free layer. This undesirable extra fluxstiffens the free layer near the edge of the sensor. The junction mustbe carefully engineered to minimize this stray flux as well as thejunction resistance. Also, a junction of dissimilar metals can causeunwanted strain in the sensor. The free layer will respond to the strainunless the magnetostriction is exactly zero. Another disadvantage is thenature of hard magnetic materials, which are multi-domained. Variationin domain size and shape lead to a distribution of domain coercivity.Lower coercivity domains may rotate when subjected to external fields.Such a domain near the sensor edge could cause domain wall formation inthe active sensor and failure.

[0006] An alternative method of stabilization is to use an “exchangetab” design. In this case, the free layer is overlaid with a pinningmaterial layer, which pins it in the proper direction. This layer iscalled an “exchange tab layer,” and it both protects against theformation of edge domains and helps bias the sensor properly. There areseveral advantages to the use of an exchange tab over abutted junction.There is no junction to produce stray magnetic flux or junctionresistance. Also, the lack of a junction of abutted, dissimilar metalsmakes it less likely to produce high strain within the sensor.

[0007] The resistance of a spin valve sensor depends upon the relativeangle between the magnetic moments of the free and pinned soft layers.To maximize the sensitivity and obtain a linear output signal, it isnecessary to bias the free layer. An ideal bias condition is when thefree layer is biased such that its magnetic moment is perpendicular tothe magnetic moment of the pinned layer in the absence of an appliedmagnetic field. Since the pinned layer in the spin valve and outerportions of the free layer are preferably oriented perpendicular to eachother, these magnetic orientations or pinning directions are typicallyestablished by separate thermal anneals, each in the presence of adifferently oriented magnetic field. One method to achieve this is tochoose pinning materials having differing blocking temperatures forpinning the pinned layer and for biasing the free layer. The pinningdirection of the material with the higher blocking temperature isestablished first. A second anneal sets the pinning direction of theother material without affecting the first. A disadvantage of thisapproach is that there are few pinning materials with blockingtemperature sufficiently high to use in a recording head. Rotation ofthe pinning direction can occur at temperatures near the blockingtemperature, leading to long-term reliability issues. Use of a secondmaterial with lower blocking temperature reduces the sensor's thermalstability, since the lowest blocking temperature determines the maximumuseable temperature.

SUMMARY OF THE INVENTION

[0008] Methods of fabricating spin valve sensors in accordance with theinvention include forming a pinning layer from an antiferromagneticmaterial and forming a synthetic antiferromagnet adjacent the pinninglayer. A free ferromagnetic layer is formed, and exchange tabs areformed adjacent outer portions of the free ferromagnetic layer forbiasing the free layer. The exchange tabs are formed from the sameantiferromagnetic material as the first pinning layer. Then, themagnetic moments of the synthetic antiferromagnet are set, and themagnetic moment of the free ferromagnetic layer is biased, during asingle anneal in the presence of a single magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a simplified diagram of a storage system using a spinvalve sensor in accordance with the present invention.

[0010]FIG. 2 is a diagrammatic air bearing surface view of a first spinvalve sensor embodiment fabricated in accordance with the presentinvention.

[0011]FIG. 3 is a diagrammatic air bearing surface view of a second spinvalve sensor embodiment fabricated in accordance with the presentinvention.

[0012]FIG. 4 is a diagrammatic air bearing surface view of a third spinvalve sensor embodiment fabricated in accordance with the presentinvention.

[0013]FIG. 5 is a plot of resistance change versus applied magneticfield for a bottom spin valve with and without exchange tabstabilization.

[0014]FIG. 6 is a flow diagram illustrating methods of fabricating spinvalve sensors in accordance with the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

[0015] The present invention includes new giant magnetoresistive (GMR)spin valve sensors which may be used in a data storage system such asdata storage system 100 shown in FIG. 1, as well as methods offabricating the spin valve sensors. System 100 includes storage medium112 such as a magnetic disc,

[0016] which is rotated by motor 114. An actuator 116 is coupled to aslider 118 which is used to position a spin valve sensor (not shown inFIG. 1) or other types of magnetoresistive sensors over a surface 120 ofdisc 112. Actuator 116 includes actuator arm 122, which is attached toslider 118 via suspension 124. A controller 126 controls positioning ofslider 118. The spin valve sensor operates by receiving a sense (orbias) current I from a current source on read back circuitry 128.Variations in a magnetic field applied to the sensor due tomagnetization of disc 112 cause a change in the electrical resistance ofthe sensor. This change in electrical resistance is detected withreadback circuitry 128 which responsively provides data output.Operation of spin valves is known in the art and is described, forexample, in U.S. Pat. No. 4,949,039, issued Aug. 14, 1990 to Grunberg,which is hereby incorporated by reference.

[0017] FIGS. 2-4 are diagrammatic air bearing surface views of spinvalve sensors 200, 300, and 400 in accordance with exemplary embodimentsof the present invention. Sensors 200, 300, 400 and 500 are embodimentsof sensors, which can be included on slider 118 (shown in FIG. 1).Sensor 200 illustrated in FIG. 2 includes antiferromagnetic pinninglayer 210, synthetic antiferromagnet 220, spacer layer 230, free layer240 and antiferromagnetic exchange tabs 250. Other layers or componentsof the type known in the art can also be included in spin valve 200, butare omitted from FIG. 2 to simplify the illustration. For example, spinvalve 200 can include seed layers if desired. Further, althoughelectrical contacts or leads are not shown in FIG. 2, those of skill inthe art will recognize that electrical leads will be included in thespin valves of the present invention.

[0018] In order to increase the stiffness of the “pinned layer”, thefrequently utilized single layer is replaced by a “syntheticantiferromagnet” (SAF) 220 as is known in the art. SAF 220 includes twosoft ferromagnetic layers 270 and 290, separated by an extremely thinmetal spacer layer 280, which can be for example ruthenium. Layer 270 isoften referred to as the “pinned layer” and is the layer adjacent to theantiferromagnetic pinning layer 210. Layer 290 is often referred to asthe “reference layer”, and is the layer closest to the free layer 240.The exchange coupling between pinned layer 270 and reference layer 290is an oscillatory function of thickness of the metal spacer layer 280.For certain thickness, the coupling can be strongly antiferromagnetic.In this case, the two magnetic layers' magnetization vectors point inopposite directions (represented by reference directions 292 and 294)and therefore have a very small net magnetic moment. An external fieldexerts a torque proportional to the net moment, so this torque must inturn be small. The result is very stiff pinned layer 290 that does notreadily respond to external fields.

[0019] The resistance of the sensor depends on θ, the relative anglebetween magnetic moment 296 of the free layer and magnetic moment 294 ofreference layer 290, wherein R(θ)=R_(min)+ΔR(1−cos θ)/2. There is anintrinsic exchange coupling between reference layer 290 and free layer240 that makes it energetically favorable for the magnetic moment of thefree layer to rotate parallel to the magnetic moment of the referencelayer (θ=0). In this configuration, the sensitivity is very low, sincedR/dθ=0. To maximize the sensitivity and obtain a linear output signal,it is desirable to properly “bias” the free layer. As discussedpreviously, the ideal bias condition is where the magnetic moment 296 ofthe free layer is perpendicular to the magnetic moment 294 of thereference layer because dR/dθ reaches its maximum value, of ΔR/2.

[0020] In a SAF, the orientation of pinned layer 270 can be manipulatedby variation of the relative thickness of pinned layer 270 and referencelayer 290, and with the application of a magnetic field. For example, ifpinned layer 270 is thinner than reference layer 290, and if the appliedfield is not too large, reference layer 290 will align with the fieldwhile pinned layer 270 will align antiparallel. In accordance withembodiments of the present invention, pinned layer 270 and referencelayer 290 have similar thicknesses. Thus, both will rotate approximatelyperpendicular to the applied field, while free layer 240 orientsparallel with the applied field. This makes it possible, with a singleanneal in the presence of a magnetic field, to simultaneously establishpinning directions in the spin valve and in the exchange tabs which areperpendicular to each other. Since a single anneal can set both pinninglayer 210 and exchange tabs 250, there is no necessity to use twodifferent antiferromagnetic materials with dissimilar blockingtemperatures.

[0021] Thus, in accordance with embodiments of the present invention,the thicknesses of pinned layer 270 and reference layer 290 of SAF layer220 are substantially the same, and antiferromagnetic pinning layer 210and antiferromagnetic exchange tabs 250 are made from the same materialsuch that they each exhibit substantially the same blocking temperature.The result is that the orientation of the magnetic moments 292 and 294of pinned and reference layers 270 and 290 can be pinned in directionsantiparallel to one another, and the orientation of magnetic moment 296of free layer 240 can be biased in a direction perpendicular to themagnetic moment of reference layer 290 with a single anneal in thepresence of field H_(ANNEAL) in direction 298.

[0022] In exemplary embodiments, AFM pinning layer 210 and AFM exchangetabs 250 are a manganese (Mn) based antiferromagnetic alloy. In someembodiments, nickel manganese (NiMn) is used for pinning layer 210 andexchange tabs 250. In these embodiments, the composition of the NiMn isusually between about 45 and 65 atomic percent Mn. However, in otherembodiments, instead of NiMn, the pinning material used includes PtMn,RhMn, RuRhMn, CoO, NiO, Fe₂O₃ or other known pinning materials. Inexemplary embodiments, pinning layer 210 and exchange tabs 250 are NiMnhaving a thickness of between about 80 Å and 300 Å. However, the presentinvention is not limited to a particular pinning material or pinningmaterial thickness.

[0023] In exemplary embodiments, SAF 220 utilizes either Co, CoFe, orCoNiFe for pinned layer 270 and reference layer 290. For example, in oneembodiment, layers 270 and 290 are layers of Co or CoFe havingthicknesses between about 15 Å and 35 Å. However, other materials can beused as well. As discussed above, the thicknesses of layers 270 and 290are preferably substantially the same. Metallic spacer layer 280positioned between reference layer 290 and pinned layer 270 can be avariety of different materials. In some embodiments, spacer layer 280 isa layer of Ru having a thickness of between about 7 and 12 Å. Syntheticantiferromagnets are known in the art and are described, for example, inU.S. Pat. No. 5,583,725 to Coffey et al. which was used issued Dec. 10,1996 and is entitled, “SPIN VALVE MAGNETORESISTIVE SENSOR WITHSELF-PINNED LAMINATED LAYER AND MAGNETIC RECORDING SYSTEM USING THESENSOR.”

[0024] Spacer layer 230 can be any of a wide variety ofnon-ferromagnetic materials. In an illustrative embodiment, spacer layer230 is Cu, which has low electrical resistivity. By way of example,spacer layer 230 can be a layer of Cu having a thickness of about 33 Å.However, other non-ferromagnetic materials can be used for spacer layer230, for example, Ag, Au, and CuX (where X is Ag, Ru or Rh, forexample).

[0025] Free layer 240 is a ferromagnetic layer whose magnetizationvector 296 is biased by exchange tabs 250, but remains unpinned suchthat, in the presence of a magnetic field to be sensed, themagnetization of free layer 240 is caused to rotate so that it is atleast partially anti-parallel to the direction in which themagnetization vector of reference layer 290 is constrained. Free layer240 can be a single or multi-layered structure. For example, free layer240 can be a layer of NiFe or a bi-layer of NiFe/CoFe. Otherferromagnetic materials can be used for free layer 240 as is known inthe art.

[0026]FIG. 3 is a diagrammatic air bearing surface view of a top spinvalve 300 in accordance with an alternate embodiment of the presentinvention. Spin valve 300 includes antiferromagnetic pinning layer 310,synthetic antiferromagnet 320, spacer layer 330, free layer 340 andantiferromagnetic exchange tabs 350. Like spin valve 200 illustrated inFIG. 2, synthetic antiferromagnet 320 includes pinned layer 370, spacerlayer 380 and reference layer 390. Also like spin valve 200, layers 370and 390 of the synthetic antiferromagnet preferably have substantiallyidentical thicknesses. Another similarity between spin valve 300 andspin valve 200 is that the material for antiferromagnetic pinning layer310 and antiferromagnetic exchange tabs 350 is preferably the same.

[0027] Since spin valve 300 is a top spin valve, antiferromagneticexchange tabs 350 and free layer 340 are formed on substrate 305 first.Then, after formation of spacer layer 330, synthetic antiferromagnet 320and antiferromagnetic pinning layer 310 are formed. With the thicknessesof pinned layer 370 and reference layer 390 of synthetic antiferromagnet320 being substantially the same, and with the same antiferromagneticmaterial used for pinning layer 310 and exchange tabs 350, theorientations directions 392, 394 and 396 of the magnetic moments ofpinned layer 370, reference layer 390 and free layer 340 can beestablished with a single anneal in the presence of magnetic fieldH_(ANNEAL) (in direction 398 parallel to direction 396). The materialsand thicknesses of the various layers in spin valve 300 can be the sameas those discussed above with reference to spin valve 200.

[0028]FIG. 4 is a diagrammatic air bearing surface view of spin valve400 in accordance with yet other embodiments of the present invention.Spin valve 400 is a combination of a bottom spin valve and top spinvalve, and is frequency referred to as a dual spin valve. Spin valve 400includes antiferromagnetic pinning layer 410, synthetic antiferromagnet420, spacer layer 430, free ferromagnetic layer 440 andantiferromagnetic exchange tabs 450 similar to those included in spinvalve 200 illustrated in FIG. 2. Again, synthetic antiferromagnet 420includes pinned layer 470, spacer layer 480 and reference layer 490which are of similar materials and thicknesses to those discussed above.Also as discussed above, antiferromagnetic pinning layer 410 andantiferromagnetic exchange tabs 450 are preferably made of the samepinning material having the same blocking temperature.

[0029] The dual spin valve 400 differs from spin valve 200 in that itincludes spacer layer 505 positioned on top of free layer 440, syntheticantiferromagnet 508 positioned on top of spacer layer 505 andantiferromagnetic pinning layer 525 positioned on top of syntheticantiferromagnet 508. As with the previous embodiments, reference layer510 and pinned layer 520 of synthetic antiferromagnet 508 are separatedby a spacer layer 515 and have substantially the same thicknesses.Likewise, antiferromagnetic pinning layer 525 is formed with the samematerial as exchange tabs 450 and pinning layer 410. Thus, during asingle anneal in the presence of an external magnetic field H_(ANNEAL)(in direction 498), the directions 492, 494, 496, 507 and 522 of themagnetic moments of layers 470, 490, 440, 510 and 520 can beestablished.

[0030] Two sheet film samples were prepared to demonstrate the methodsof fabricating spin valve sensors of the present invention. The firstsheet film was a bottom spin valve with a synthetic antiferromagnetpinned layer and with the upper most layer forming the free layer. Thesecond sample was prepared under identical conditions, but with an extralayer of antiferromagnetic material deposited on to the free layer toact as the exchange tabs. The two samples were annealed once, togetherunder identical conditions. The results show that the exchange tabsample is pinned along the applied field, while the bottom spin valve ispinned in a direction perpendicular to the applied field as shown inFIG. 5 which plots the resistance change versus applied magnetic fieldfor these films. The sharp transition seen in the spin valve isbroadened in the exchange tab sample. This is because the “free layer”is now biased by the overlaid antiferromagnetic exchange tabs. A fit tothe data indicates the pinning field to be 223 Oe oriented within 3° ofnormal to the pinned layer. The anneal was repeated twice on the samesample, and the pinned layer showed no sign of rotation.

[0031] The methods of the present invention of fabricating spin valvesensors are illustrated in the flow diagram of FIG. 6. As illustrated atblock 610 of FIG. 6, a first pinning layer is formed from anantiferromagnetic material. As shown at block 620, a first syntheticantiferromagnet is formed adjacent and in contact with the first pinninglayer. At blocks 630 and 640, the method is shown to include forming afirst spacer layer adjacent the first synthetic antiferromagnet andforming a free ferromagnetic layer adjacent the first spacer layer. Atstep 650, exchange tabs are formed adjacent outer portions of the freeferromagnetic layer for the purpose of biasing that layer. Asillustrated at step 660, the magnetic moments of the first syntheticantiferromagnet and the magnetic moment of the free ferromagnetic layerare oriented (set or biased) during a thermal anneal in the presence ofa single magnetic field.

[0032] These steps can be varied as described above to fabricate topspin valves, bottom spin valves and dual spin valves. Also, the stepsshould be interpreted in view of the previous discussion such that thepinned and reference layers of the synthetic antiferromagnet(s) arepreferably of the same thickness. Also, the antiferromagnetic materialused to form the exchange tabs and the first pinning layer arepreferably the same as described previously. Obviously, the steps can beperformed in the order necessary to fabricate the different types ofspin valves, and additional steps can be added as needed.

[0033] Although the present invention has been described with referenceto preferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A storage system for storing information,comprising: a magnetic storage medium; means for reading informationfrom the magnetic storage medium.
 2. A method of fabricating a spinvalve magnetoresistive sensor comprising: forming a first pinning layerfrom an antiferromagnetic material; forming a first syntheticantiferromagnet adjacent the pinning layer; forming a first spacer layeradjacent the first synthetic antiferromagnetic; forming a freeferromagnetic layer adjacent the first spacer layer; forming exchangetabs adjacent outer portions of the free ferromagnetic layer, whereinthe exchange tabs are formed from the same antiferromagnetic material asthe first pinning layer; and orienting magnetic moments of the firstsynthetic antiferromagnet and of the free ferromagnetic layer during asingle anneal in the presence of a single magnetic field.
 3. The methodof claim 2, wherein forming the first synthetic antiferromagnetcomprises: forming a pinned ferromagnetic layer adjacent the firstpinning layer; forming a metal spacer layer adjacent the pinnedferromagnetic layer; and forming a reference ferromagnetic layeradjacent the metal spacer layer such that the reference ferromagneticlayer is positioned between the first spacer layer and the metal spacerlayer.
 4. The method of claim 3, wherein forming the first syntheticantiferromagnet further comprises forming the pinned ferromagnetic layerand the reference ferromagnetic layer such that they have substantiallythe same thicknesses.
 5. The method of claim 4, wherein orientingmagnetic moments of the first synthetic antiferromagnet and of the freeferromagnetic layer during the single anneal in the presence of thesingle magnetic field further comprises annealing the spin valvemagnetoresistive sensor in the presence of the single magnetic fieldoriented in a first direction to set a magnetic moment of the pinnedferromagnetic layer in a second direction perpendicular to the firstdirection, to set a magnetic moment of the reference ferromagnetic layerin a third direction perpendicular to the first direction andantiparallel with the second direction, and to bias a magnetic moment ofthe free ferromagnetic layer in a fourth direction parallel to the firstdirection and perpendicular to the second and third directions.
 6. Themethod of claim 5, wherein the first synthetic antiferromagnet is formedon the first pinning layer, the first spacer layer is formed on thefirst synthetic antiferromagnet, the free ferromagnetic layer is formedon the first spacer layer and the exchange tabs are formed on the freeferromagnetic layer.
 7. The method of claim 6, and further comprising:forming a second spacer layer on a central portion of the freeferromagnetic layer between the exchange tabs; forming a secondsynthetic antiferromagnet on the second spacer layer; and forming asecond pinning layer on top of the second synthetic antiferromagnet,wherein the second pinning layer is formed from the sameantiferromagnetic material as the first pinning layer and the exchangetabs.
 8. The method of claim 5, wherein the free ferromagnetic layer isformed partially on the exchange tabs, the first spacer layer is formedon the free layer, the first synthetic antiferromagnet is formed on thefirst spacer layer, and the first pinning layer is formed on the firstsynthetic antiferromagnet.
 9. A spin valve magnetoresistive sensorcomprising: a first pinning layer formed from an antiferromagneticmaterial; a first synthetic antiferromagnet adjacent and in contact withthe pinning layer; a first spacer layer adjacent and in contact with thefirst synthetic antiferromagnet; a free ferromagnetic layer adjacent andin contact with the first spacer layer; and exchange tabs adjacent andin contact with outer portions of the free ferromagnetic layer, whereinthe exchange tabs are formed from the same antiferromagnetic material asthe first pinning layer.
 10. The spin valve magnetoresistive sensor ofclaim 9, wherein the first synthetic antiferromagnet further comprises:a pinned ferromagnetic layer adjacent and in contact with the firstpinning layer; a metal spacer layer adjacent and in contact with thepinned ferromagnetic layer; and a reference ferromagnetic layer adjacentand in contact with the metal spacer layer such that the referenceferromagnetic layer is positioned between the first spacer layer and themetal spacer layer.
 11. The spin valve magnetoresistive sensor of claim10, wherein the pinned ferromagnetic layer and the referenceferromagnetic layer of the first synthetic antiferromagnet havesubstantially the same thickness.
 12. The spin valve magnetoresistivesensor of claim 11, wherein a magnetic moment of the pinnedferromagnetic layer is set in a first direction, wherein a magneticmoment of the reference ferromagnetic layer is set in a second directionantiparallel with the first direction, and wherein a magnetic moment ofthe free ferromagnetic layer is biased in a third directionperpendicular to the first and second directions.
 13. The spin valvemagnetoresistive sensor of claim 12, wherein the first syntheticantiferromagnet is formed on the first pinning layer, the first spacerlayer is formed on the first synthetic antiferromagnet, the freeferromagnetic layer is formed on the first spacer layer and the exchangetabs are formed on the free ferromagnetic layer.
 14. The spin valvemagnetoresistive sensor of claim 13, and further comprising: a secondspacer layer formed on a central portion of the free ferromagnetic layerbetween the exchange tabs; a second synthetic antiferromagnet formed onthe second spacer layer; and a second pinning layer formed on top of thesecond synthetic antiferromagnet, wherein the second pinning layer isformed from the same antiferromagnetic material as the first pinninglayer and the exchange tabs.
 15. The spin valve magnetoresistive sensorof claim 12, wherein the free ferromagnetic layer is formed partially onthe exchange tabs, the first spacer layer is formed on the free layer,the first synthetic antiferromagnet is formed on the first spacer layer,and the first pinning layer is formed on the first syntheticantiferromagnet.